In reply to Tim.

This is the only API themes can really use, and if the goal is to replace this API..

Themes as we know them today will be history if Gutenberg will be complete as intended somewhere in future.

Actually Gutenberg has to be considered as a fork of WordPress as it deeply changes the whole system, abandoning “old school” themes and complex template hierarchy in favour of a a few simple json templates with “allowed blocks” definition and trying to convert some plugins to blocks and establishing a block-repository, maybe one day also with paid premium blocks.

People still fail to understand this long term concept and will argue “but Classic Editor”, but “Elementor”, but “whatever”, they will either have to abandon all that and move on with the “new” WordPress or stay behind, like some already do at 4.9.x, others as soon as Classic Editor will be phased out, or will leave to other solutions.

Interesting times.